An access attribute defines whether a component is available globally or is just public. Global components can be accessed outside the namespace. If an AppExchange vendor allows subscriber organizations to use components, they will be marked as global.
By default, components are public. This means they cannot be accessed outside of the current namespace.
The syntax with the access attribute should be as follows:
<aura:component access="global">
<!-- Optional coponent attributes here -->
<!-- Optional HTML markup -->
</aura:component>